Platelet activating factor (PAF), a potent phospholipid mediator, is synthesized by brain-resident macrophages and microglia, and secreted at neurotoxic levels during HIV-1 infection. We have previously shown that levels of PAF in cerebrospinal fluid correlate with neurologic dysfunction and immunosuppression in patients with HIV-1 associated dementia (HIV-D). Furthermore, we have shown that PAF mediates neuronal apoptosis by activation of the NMDA subtype of glutamate receptors. These findings lead us to propose that excessive production of PAF is an initiator step in HIV-1 neuropathogenesis. In this application we will determine how PAF activates brain-resident macrophages and microglia, and vulnerable neurons to induce neuronal dysfunction and death in the following specific aims: In Aim 1, we will determine whether cultures of cortical, striatal, hippocampal, and cerebellar granule neurons have different profiles of vulnerability (i.e. cell death) based on their identity (i.e. neurotransmitter/receptor subtype) and brain region. We will then determine whether PAF receptor-mediated neuronal demise is due in part to a change is NMDA receptor subunit composition using the technique of single cell antisense RNA analysis. We will repeat these experiments in organotypic slice cultures to determine if the in vitro results remain valid with an intact extracellular matrix and supporting glial cells present in an organotypic culture slice. In Aim 2, we will determine the relative contribution of PAF receptor activation in brain- resident macrophages and microglia toward the excess production of arachidonic acid, which is known to activate NMDA receptors and thereby further potentiate any effects that PAF may have on presynaptic release of glutamate. We will correlate these findings with neuronal cell death measured in cortical, striatal, hippocampal, and cerebellar granule neurons co-cultured with carbamyl (resistant to metabolic degradation) PAF-treated microglia. In Aim 3, because PAF receptor activation mediates increased neuronal GSK-3beta activity, which phosphorylates the cytoskeletal protein beta-catenin, destabilizing it and thereby targeting it for proteasomal degradation, we will determine whether in vitro and in vivo application of carbamyl PAF results in the functional consequence of decreased neurite outgrowth in vitro and a reduction in the dendritic arbor in vivo, a neuropathologic hallmark of HIV-D. Taken together, results from these studies will advance our understanding of how excess production of PAF contributes to the neuropathogenesis of HIV-1.